1. Field of the Invention
The present invention relates to a film deposition apparatus for depositing a film on a substrate by causing the substrate on a turntable to alternately pass through a source gas supply area for supplying a source gas and a reaction gas supply area for supplying a reaction gas reactable with the source gas by rotating the turntable in a vacuum chamber.
2. Description of the Related Art
So-called ALD (Atomic Layer Deposition) is known as a method for depositing a thin film such as a silicon oxide (SiO2) film on a substrate such as a semiconductor wafer (which is hereinafter called a “wafer”). Japanese Laid-Open Patent Application Publication No. 2013-222948 discloses an apparatus for implementing ALD that includes a vacuum chamber and a turntable for receiving a plurality of wafers thereon provided in the vacuum chamber and causes the plurality of wafers arranged on the turntable to alternately pass through an area to which a source gas is supplied and an area to which a reaction gas reactable with the source gas is supplied. In a top surface of the turntable, a plurality of concave portions is formed to hold the wafers therein when the wafers are fitted therein. Each of the concave portions is formed to have a diameter slightly larger than a diameter of the wafer when seen in a planar view to provide a clearance outside the outer edge of the wafer (to hold the wafer detacheably therefrom).
It is known that the wafer warps at its central part so as to rise as compared to its peripheral part immediately after being transferred into the concave portion due to nonuniformity of a temperature of the wafer and then gradually reduces its warp as the uniformity of the temperature of the wafer increases. In the meantime, because the turntable is rotated, the wafer moves toward the peripheral side of the turntable by the clearance due to a centrifugal force caused by the rotation of the turntable. In this manner, because the wafer moves while returning to a flat state from a warped state, the wafer moves while rubbing the bottom surface of the concave portion with its peripheral part, which is liable to cause particles.
To prevent this, Japanese Laid-Open Patent Application Publication No. 2013-222948 proposes a configuration of providing a pedestal to support a wafer having a planar shape smaller than that of the wafer on the bottom surface of the concave portion. According to the configuration, because the peripheral part of the wafer is prevented from rubbing the bottom surface of the concave portion, the generation of the particles can be prevented. However, the inventors of the present invention have found that when performing a process of rotating the turntable at a high rotational speed or setting a processing atmosphere at a high pressure, a phenomenon occurs that the film thickness becomes locally thick at a part of the periphery. This phenomenon is considered to occur because when the wafer moves to the peripheral side of the turntable by the centrifugal force, the outer edge of the wafer is pressed against the inner wall of the concave portion and an upper end of a groove portion formed between the side wall of the pedestal and the inner wall of the concave portion is partially enclosed by the wafer, in which a gas is enclosed.